Dan Dugan:
>> The 744 started giving me low battery warnings around sunrise. I
>> watched the display to see it switch over to the internal battery.
>> Imagine my chagrin when it failed to do that and just shut down. It
>> was the first time I've had a technical problem with the 744. It
>> reported file system errors. I ran the repair utility but it wasn't
>> able to fix the file. I sent the machine back to Sound Devices to see
>> what they could do. They explained that the voltage of lead-acid
>> batteries rises after the load is taken off, and this confuses their
>> switchover circuit. Perhaps when I'm also powering the MP-2 preamp
>> from the battery that load will stabilze it. To be continued.
>> -Dan Dugan
John Hartog:
> That is the exact problem I have had with my 722 and the various
> battery packs I have made up of AA NiMH, AA Alkaline, and D Alkaline
> batteries. It is good to know to expect the same from lead-acid. I
> don't think SD tested their "seamless" switch over mechanism very
> thoroughly. They told me a while back, they only recommend lithium,
> but I am now skeptical that even with an expensive lithium system, the
> results in the end will be the same - the continued corruption and
> loss of important recordings. I don't know, does the voltage of
> lithium not rise like other batteries after the load is taken off?
>
> My workaround has been to set the file size limit fairly small. My 722
> so far has only corrupted the last file of the session when the
> failure occurs. I have not yet tried running off an external pack
> without the attached battery installed, but that might at least close
> the final file correctly.
I've suggested a hysteresis parameter for the switchover; after the
threshold level has been reached, the external source must be X volts
above the threshold before it will switch back to it.
-Dan Dugan
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